21005989 has 8 divisors (see below), whose sum is σ = 21427200. Its totient is φ = 20588400.

The previous prime is 21005987. The next prime is 21006017. The reversal of 21005989 is 98950012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21005989 - 2¹ = 21005987 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005983) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 12787 + ... + 14335.

It is an arithmetic number, because the mean of its divisors is an integer number (2678400).

Almost surely, 2^21005989 is an apocalyptic number.

It is an amenable number.

21005989 is a deficient number, since it is larger than the sum of its proper divisors (421211).

21005989 is a wasteful number, since it uses less digits than its factorization.

21005989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1811.

The product of its (nonzero) digits is 6480, while the sum is 34.

The square root of 21005989 is about 4583.2291018451. The cubic root of 21005989 is about 275.9186424419.

The spelling of 21005989 in words is "twenty-one million, five thousand, nine hundred eighty-nine".